Addressing Nappi’s 12-year-old daughter and his 11-year-old son, Mayor Bloomberg said their father — a 17-year department veteran — would be remembered as a hero who served the city during its greatest time of need.

“Your father rushed to the firehouse. He was assigned to lower Manhattan on the darkest day in the city’s history,” Bloomberg said, recounting Nappi’s role after the 9/11 attacks. “And in the days and weeks after, he worked among the smoking rubble of the World Trade Center. You should be very proud of your father.”

Fire Commissioner Salvatore Cassano said his “heart sank” when he learned of Nappi’s death.

“I knew Richard. We worked together in the late ’90s, in lower Manhattan. He’s so full of life and you never forgot him once you met him,” Cassano said.

The gregarious lieutenant was known as “yappy Nappi” around the firehouse because he was so social, said Cassano.

The flag-draped casket of Nappi, who trained volunteer firefighters at Suffolk County Fire Academy, was delivered to St. Elizabeth Ann Seton Church atop a firetruck. About 400 firefighters, friends and family filled the church for the solemn service.